A wireless local area network (WLAN) in the infrastructure basic service set (BSS) mode has an access point (AP) for the BSS, and one or more stations (STAs) associated with the AP. The AP typically has access to or interfaces with a distribution system (DS) or another type of wired/wireless network that carries traffic in to and out of the BSS. Traffic to STAs that originates from outside the BSS arrives through the AP and is delivered to the STAs. Traffic originating from STAs to destinations outside the BSS is sent to the AP to be delivered to the respective destinations. Traffic between STAs within the BSS may also be sent through the AP where the source STA sends traffic to the AP and the AP delivers the traffic to the destination STA. Such traffic between STAs within a BSS is really peer-to-peer traffic. Such peer-to-peer traffic may also be sent directly between the source and destination STAs with a direct link setup (DLS) or a tunneled DLS (TDLS). A WLAN in independent BSS mode (IBSS) has no AP and STAs communicate directly with each other.
In an infrastructure BSS, a STA performs a scanning procedure to discover an appropriate AP/network to establish a WLAN link, usually via an association procedure. There are two basic scanning modes: passive scanning and active scanning.
With the passive scanning mode, the AP periodically transmits beacon frames to provide AP/network information to the STA. The beacon supports various functions in the system by providing an AP advertisement with a BSS identifier (BSSID), synchronization of the STAs in the BSS, capability information, BSS operation information, system parameters for medium access, transmit power limits, etc. In addition, the beacon may carry many optional information elements.
With the active scanning mode, the STA actively generates and transmits a probe request frame to the AP, receives a probe response frame from the AP, and processes the probe response frame to acquire the AP/network information.
FIG. 1 shows a general frame format for a beacon frame 100, which includes a medium access control (MAC) header 102, a frame body 104, and a frame check sequence (FCS) field 106. The MAC header 102 includes a frame control field 110, a duration field 112, multiple address fields 114-118, a sequence control field 120, and a high throughput (HT) control field 122.
The frame body 104 includes mandatory fields and information elements (IEs), including, but not limited to (not shown in FIG. 1): a timestamp field, a beacon interval field, a capability field, a service set identifier (SSID) field, a supported rates field, and one or more optional IEs, such as BSS load information. The BSS load information indicates the level of traffic loading at the BSS, and may include five relevant IEs: BSS load, including STA count, channel utilization, and admission capability; BSS available admission capacity; quality of service (QoS) traffic capability; BSS average access delay; and BSS access category (AC) access delay. With the mandatory and typical optional IEs, beacon frames may be over 100 bytes long. In a typical enterprise environment, the beacons are approximately 230 bytes long.
A goal with fast initial link setup (FILS) is to support an initial link setup time for STAs within 100 ms and to support at least 100 non-AP STAs simultaneously entering the BSS and fast link setup within one second. Because beacons may be used to provide information about the AP to the STAs at the beginning of the initial link setup process, beacons may include information to facilitate a fast link setup to satisfy the specified functional requirements.
The FILS process consists of five phases: (1) AP discovery; (2) network discovery; (3) additional timing synchronization function (TSF); (4) authentication and association; (5) higher layer IP setup.